Yosemite Ibook taking extra long to highlight

Hi,

I run a MacBook Pro Late 2011, 8GBs 1333MHz DDR3, 2,4 Intel i5, with Yosemite 10.3.3 and iBooks 1.1.1. (600).

When I highlight my ebooks with multiple colors and underlinings, after many pages using all of them the app starts to get slower and slower to apply each one of this very simple task.

I don't know if it can't handle many combinations, or many highlights, or if it has any kind of limit we should abide to. All I know is that after working with about 2 from 10 chapters, it started to take about 4 to 5 seconds to apply each one, and this is driving me nuts!

First I've thought it could be the sync feature, and I turned this function off hoping this would help, but it didn't. Then I thought it could be a memory overflow, and I quitted all extra applications around, but still got the same annoying waiting...

I know I don't run a Ferrari, but my system (which works fine with many other applications) should take this task A LOT faster.

Obs: At my iOs8 version, we are still stuck with that annoying "highlight everything" issue... come on, guys, when are you going to allocate a capable team to take care of this CORE software?

Alexandre