Not really a major issue, but it is funny thinking about it.

Several programmes do it I imagine, but isn't it hilarious when Doctor Who references another show which also references Doctor Who?

Confused? hehe, here's an example.

In "Father's Day", Rose describes Pete as a bit of a "Del Boy", which (in my mind anyway) is a reference to the character from Only Fools.

In "Only Fools", a few references are made to Doctor Who in numerous episodes; (the faulty child doll that cries out "Exterminate", or Racquel mentioning she had a minor role in the show as a "Lizard creature").

Another example;

The Doctor also makes a reference to EastEnders in "The Impossible Planet" ("This is the best Christmas Walford's ever had!")

I can't think of any specific examples but I'm sure EastEnders has made references to Doctor Who sometime in its history.

Don't these conflicting show realities create some sort of paradox?

As I said, its a minor niggle but its funny!

Any other examples?

Bradley in Eastenders is meant to be a big Who fan; I believe he once won a pub quiz by naming all ten actors who've played him, in order

Also, the Doctor has referred to some Kylie song or other in the past - and of course Kylie will be appearing at Christmas (not playing herself), so that'll be an odd one.

thought Bradders was a Trekkie

I'm sure I remember Arthur Fowler settling down to watch Coronation Street.

This sort of device is used often in fiction of all sorts. Especially, in books where more complicated fancies can imagined. (Where a character is aware they are a character in a book and can argue with the author that the book is not as good as some other author's book, for example)

Plus EastEnders being on the telly in 'Army Of Ghosts' with Barbara Windsor making a cameo.
Yeah Zoe Slater once mentioned the TARDIS, and Darren Miller said he was going to watch a Doctor Who DVD. It also had a character in the late '80s who was a Doctor Who fan.

How all of the above fits in with 'Dimensions In Time' is anyone's guess!
There's a way around it: The version of 'Only Fools & Horses' broadcast in the Doctor Who Universe is slightly different to ours and didn't have those references. Plus it presumably didn't feature Roger Lloyd-Pack, or else everyone would have said to John Lumic "Blimey! You're the spitting image of Trigger!" Even though that was in another Universe. (My brain hurts!)

Likewise the 'Only Fools...' Universe has a TV show called Doctor Who which didn't mention Del Boy, etc, allowing both Universes to harmoniously co-exist without shattering the space-time Multiverse... or something.

Ahhh well thats okay then I'll sleep easily tonight.

And Sarah Jane Adventures referencing High School Musical. And in High School Musical they reference... er.. perhaps not.