Mmm.. for me seems not. I have 1440x900, and for me window size the same size as on my shoot: i.e. about 2/3 by X, and 1/3 are "free".When the window opens it resizes to the maximum width available.
I can't resize window to the minimum when its all compiled with disabled CHILD_MinWidht, 160 , but i can resize it bigger. And i even can move it over the borders, from both sides of screen (i.e. begining of window put to the left side, and resize it till end to the right side). Can move it to any direction and resize as i wish: no bugs or distorted borders or gadgets.It's not terribly obvious, but the gadgets are all getting truncated at the window border. If I try to resize it, it only lets me resize it to bigger sizes (bigger than the width of my screen).
1440x900. I test now CHILD_MinWidth, 1600, and while whole window resizes and fits to the full screen , i have some small glitch which override right border. But once i make active any window, its refreshes to looks ok. But no gadgets corruption or so at all, just a border line. Maybe you also didn't have it, jut you can't see it. Or maybe its all depends on what theme you/i use (for me silver green, for you seems default one). Or maybe some wb settings somethere. But cleary that i can't normally reproduce what you have, but roots of my "overlap border line" imho the same as for you when you loose everything include gadgets.What resolution are you running in? Perhaps you need to make the button text longer for the resulting gadget to be wide enough to show the problem?
For my "1600" test its imho ok and fine that it give me ability to only resize to the bigger sizes: because i set 1600 minimum. But if i set CHILD_MinWidth, less that 1440, then its all fits ok, no overlaping or anything like that.If I try to resize it, it only lets me resize it to bigger sizes (bigger than the width of my screen).
mm.. rechecked your second attach 10 times and still can't get what you try to show thereYes, at least that's what I would expect from a user interface perspective. A button bar with no visible buttons is clearly not intuitive! I'd argue the same for when there are too many buttons to fit - it's not obvious there are further buttons that aren't currently visible.
speedbarbug2.jpg

Anyway, there then 2 moments:
1). Overlaping of right border in some conditions (when the Child_MinWidth are bigger that actual screensize) - so that kind of bug. As it should just resizes to the full screen with no overlaping. But pressing on the window and allowing to resize it only bigger imho right and as should be. nope ?
2). Suggestion about "to show the speedbar buttons with moved-truncated text in, but not delete it fully" already reported few years ago in BZ 5313 by Ssolie, here is text of BZ:
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The speedbar.gadget may hide buttons when there is not enough space
to render them all. There is also a scrolling feature that will scroll
the space to show the hidden buttons.
What is missing is a way to notify the user that buttons are hidden.
There is no visual indication at all.
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So while with second one its reported already (right?) , with first one its all still not clear. Did we have the same and only one bug, or you also have something else ..
ps. And i can't at all "scroll" anything in your example btw, not with left-shift-lmb, not with right-shit-lmb. How and what i can scroll there ?