I wouldn't take what any inspector or realtor told me as gospell. You need an independent contractor whose well versed in windows to check out your supposed problem and give you a written answer.
A realtors job is to sell your home. They will tell you just about anything to get you to fall in line with what they think the buyer wants...they don't care about your pocketbook only their own.
I've dealt with enough inspectors over the years to know that for the most part they are a useless lot. There's a few around who actually do a good job. Most count the number of doors and windows,calculate the sq. footage and flip a few switches to see if they work. They then write up a report which every new home buyer belives is gospell as well as every banker and send out a nice hefty bill for their 20 minutes of work.
In the 7 houses I've owned in 5 different states,I've only had one inspection that was worth anything. The guy was very good. Actually crawled up on the roof,crawled into the crawl spaces,checked ALL the switches and outlets with a meter,ran the swamp cooler and the air conditioner,as well as the heater, he inspected the plumbing inside and out including the pool. He was worth every cent we paid for him.
Conversely I had one done on the house we are in now and other than tell us how much square footage there was and that the place had "alot of windows" the guy missed the fact that the place needed a new roof, that the chimney needed to be repointed, that the furance was near ready to die, that the water heater was past it's prime, that the plumbing was prehistoric, that the wiring was in need of replacement.....they did on pick up on the oil tank being in the ground...the bank was worried about a leak so the inspector tested for leakgage by digging a inch down where the tank was and sent the sample to a lab.....sorry but any leak was not going to show at the surface....for that we lab work we paid a heft 200 dollars.
My point is that insepctors vary widely. What's important to one isn't to another. When it starts affecting your bottom line the only way to fight back is to find a pro who sides with you OR spend the bucks to change it. I'd be more incline to find a pro to agree with you as long as what is there is to your local fire code.

If the windows are double-hung and each sash can be tilted and removed for washing, remove them and see if the bottom of each sash has properly engaged the balance mechanism in the jamb of the frame.

If a double-hung window sash won't stay up after opening, it is defective and this is the most common and most easily repaired cause. The fact that they all act the same way is a pretty good indication that someone has taken them out and failed to replace them correctly.

I've found out it was from caulking. The previous owner is famous for his caulk jobs around the house. DH and I will discuss it. I'm tempted to leave it.