shinkan That is because Construct uses power of 2 for spritesheeting. So, in your case, 3 64x64 images are smaller than one 128x128 image. Also, two 258x17 can`t be on a sheet that is lower size than 512, because 512/2 = 256, your image is 2 pixels too wide. And considering that Construct uses 1 pixel each side for sheeting, the max size for a 512x512 sheet would be 254.
Hope I could help you, and sorry for my "engrish", I am Brazilian.
I'm all aware how C2 uses power of 2 texture, you don't need to explain that to me.
I'm not complaining, C2 does a great job with sprite sheets, but occasionally it's hard to predict what results you will get.
And it still does not explain why textures make with proper size are sometimes sprite sheeted and sometimes not.
In my current project I have a sprite with 14 frames, each one is 1022x254 - made them like that so they can be all placed in nice sprite sheets after export. And again sometimes it will make 1 sprite sheet 2048x2048 (which fits all frames all together), sometimes it will make 2 sheets 1024x1024, and rarely it makes 14 separate images 1022x254. and even more very rarely i got few 1024x1024 sheets with only two images inside.
So yeah. I only try to understand how C2 decides what and when will be sprite sheeted.