Here I attempt the basic trim on a circle, to create a sort of "hat"
I create a circle with 1inch diameter
I put a horizontal line through it long enough to create intersecting points
I select the Trim function (not trim two)
I select the horizontal line as limiting entity, the line turns a green color
Next I am told to Select entity to trim
I then go to select the top half of the circle to complete the trim, and it does nothing.
I have attempted saving and reloading the file, with no luck.
It does, however, work as expected with lines.
Compiler: GNU GCC 4.9.1
Compiled on: Sep 23 2016
Qt Version: 5.4.1
Boost Version: 1.60.0
Also considering the original object, circle with a line longer than the diameter through the circle, I found some interesting reactions when using the trim feature.
I select the horizontal line as limiting entity.
I then proceed to select the top half of the circle to trim the bottom half.
When selecting, I do see a reaction from the program.
The reaction is hard to explain: Basically I can see a reaction of the program on the pixels (they shift or stutter), but do not behave as expected (expected the pixels to disappear), and the behavior I do see as noted is very very minute.
I tried your suggestion. I selected the circle, and deleted, and it is now completely gone.
I see what you mean. Though, there is certainly only 1 circle object.
I did also attempt going through the motions (or commands) of performing the trim function, and after deleting the circle. It still deletes the entire and only circle leaving me with only a line. So I believe that it could have been that it creates a copy of itself after the trim is done. But this is not the case.
I am at a loss here. I've created a new drawing and attempted numerous ways to trim with numerous object setups (i.e. multiple ways of drawing my "hat") and it worked as expected (albeit with numerous clicks around the trimmed object) with each iteration. I'll have to look into screen recording to really show what's going on. I will update later.