Why is the "select text color" in Edit Post changes my font instead??? I am confused!

I am going mad. I have spent countless hours trying to work this out. If anyone can help me, I would be so grateful.

I used to be able to change the text color in my posts by highlighting the text in question and clicking the "select text color" drop down menu with the colored squares in the visual tab of "edit post" - this would change my text to the color I select (and when I clicked on the HTML tab I would see the corresponding HTML code such as <span style="color: #33cccc;"> for the color blue for example)

Now, for some bizarre reason, when I select the text I want to color and click the "select text color" on the visual tab, it is actually my text font that changes instead and the code I see in the HTM tab is this:
<span style="font-family: mceinline;">...</span> instead of <span style="color: #33cccc;"
this happens no matter what color I choose!

And to make things even more confusing, sometimes (but not always), a random part of my post which is NOT the text I highlighted gets colored in the color I selected.

So now, I have to manually color the desired text in my post using the HTML tab instead of the visual tab...which is such a nightmare because I am so incompetent at that sort of stuff!

Is this making sense to anyone? please help me!

Do I have a bug somewhere?
thanks - Dee