The text of potion effects disappears when you move undamaged enchanted items in the inventory. Picking up damaged enchanted items produces a graphical glitch instead.
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duplicates 1
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I tried doing what you describe and could not replicate the result. I tried in both creative and survival modes. I'm also in an SSP world. Did you experience this in SMP?
It also happens if you click on potions.
To Matthew Isaac: This is what I experience
Drink a potion
Click on another potion/enchanted tool
The effect bar (like Fire Resistance) becomes transparent, but you keep the potion effects
Yup, I followed what Asdf said, and can confirm that while holding down mouse button the potion effect box was transparent. Once I released the mouse the box returned to normal, clearly showing the effect and time remaining.

Added screenshot.

Performing this with an undamaged enchanted items produces the old effect still. Picking up damaged enchanted items now produces a graphical glitch.
In my experience this and also text in your inventory text turns white while the potion text disappears, but really I think Minecraft is swapping the colours of the text somehow.

Forward resolving to MC-35643 as there are already more other duplicates.
It also happens when you don't hover over an item sometimes.