Some glitches in the simualtion waveforms

As I said before, you need your simulation input stimulus to meet the setup and hold requirements of the input pins. I think that is what FvM was referring to.

And I still think what you are calling glitches are not actually glitches. People usually use the word "glitch" for a disturbance on a signal that is less than a clock cycle long. I suspect that when you zoom in on your simulation waveforms you will see that whatever is happening on the problem output is a pulse that lasts for at least one full clock cycle.

Because you are doing a timing simulation, you are seeing the effects of everything that changes in the place and route. When you change anything in the source code including changing whether you have one component or both of them present, there is some randomness to the resulting change in the exact timing. It might be only coincidence that it appears to work with one component but not with both components. If you have any timing violations reported by TimeQuest or the Classic Timing Analyzer (assuming you have proper timing constraints), it is not surprising to get unexpected results in timing simulation.